Not possible to use alarm with anomaly detector within alarm widget of a Cloudwatch dashboard

Currently I cannot find explicit support of anomaly detectors in CW Alarms in CDK, only this related issue: https://github.com/aws/aws-cdk/issues/6562

Issue’s author created SO thread, in which following working snippet can be found:

anomaly_cfnalarm = cw.CfnAlarm(self, "AnomalyAlarm",
                               actions_enabled=True,
                               alarm_actions=[slack_topic.topic_arn],
                               alarm_description="<..>",
                               alarm_name="AnomalyAlarm",
                               comparison_operator="LessThanLowerOrGreaterThanUpperThreshold",
                               datapoints_to_alarm=1,
                               evaluation_periods=1,
                               insufficient_data_actions=[slack_topic.topic_arn],
                               metrics=[
                                   cw.CfnAlarm.MetricDataQueryProperty(
                                       expression="ANOMALY_DETECTION_BAND(m1, 2)",
                                       id="ad1"
                                   ),
                                   cw.CfnAlarm.MetricDataQueryProperty(
                                       id="m1",
                                       metric_stat=cw.CfnAlarm.MetricStatProperty(
                                           metric=cw.CfnAlarm.MetricProperty(
                                               metric_name=anomaly_detector.metric_name,
                                               namespace=anomaly_detector.namespace
                                           ),
                                           period=core.Duration.minutes(5).to_seconds(),
                                           stat="Sum"
                                       )
                                   )
                               ],
                               ok_actions=[slack_topic.topic_arn],
                               threshold_metric_id="ad1",
                               treat_missing_data="breaching"
                               )

This code works by itself. But if we reference this alarm inside AlarmWidget and add this widget to Dashboard, then synth passes, but deployment fails.

Reproduction Steps

1. Define resources similar to this

anomaly_detector = aws_cloudwatch.CfnAnomalyDetector(
            self,
            id="Error anomaly detector",
            metric_name="Errors",
            namespace="AWS/Lambda",
            stat="Average",
            dimensions=[
                aws_cloudwatch.CfnAnomalyDetector.DimensionProperty(
                    name="FunctionName",
                    value=some_function.function_name
                )
            ]
        )

error_alarm = aws_cloudwatch.CfnAlarm(
            self,
            id="Error alarm",
            metrics=[
                aws_cloudwatch.CfnAlarm.MetricDataQueryProperty(
                    expression="ANOMALY_DETECTION_BAND(m1, 2)",
                    id="ad1"
                ),
                aws_cloudwatch.CfnAlarm.MetricDataQueryProperty(
                    id="m1",
                    metric_stat=aws_cloudwatch.CfnAlarm.MetricStatProperty(
                        metric=aws_cloudwatch.CfnAlarm.MetricProperty(
                            metric_name=anomaly_detector.metric_name,
                            namespace=anomaly_detector.namespace
                        ),
                        period=300,
                        stat="Average"
                    )
                )
            ],
            evaluation_periods=2,
            threshold_metric_id="ad1",
            comparison_operator="GreaterThanUpperThreshold"
        )

error_rate_alarm_widget = aws_cloudwatch.AlarmWidget(
            alarm=error_alarm,
            height=6,
            width=6,
            title="Collector error rate alarm status",
            region=core.Aws.REGION
        )

dashboard = aws_cloudwatch.Dashboard(
            self,
            id="Monitoring dashboard",
            dashboard_name="foobar"
        )
dashboard.add_widgets(error_rate_alarm_widget)

1. Try to deploy

Error Log

The dashboard body is invalid, there are 2 validation errors:
[
  {
    "dataPath": "/widgets/0/properties",
    "message": "The metric widget should have specified a region and a data source or an alarm annotation"
  },
  {
    "dataPath": "/widgets/0/properties",
    "message": "Should have required property 'metrics' or 'insightRule'"
  }
] (Service: AmazonCloudWatch; Status Code: 400; Error Code: InvalidParameterInput; Request ID: f2fb5110-095b-495e-aeec-7d8db031e65b)
        new Dashboard (/tmp/jsii-kernel-fioN2e/node_modules/@aws-cdk/aws-cloudwatch/lib/dashboard.js:38:9)
        \_ obj._wrapSandboxCode (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7853:49)
        \_ Kernel._wrapSandboxCode (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:8313:20)
        \_ Kernel._create (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7853:26)
        \_ Kernel.create (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7600:21)
        \_ KernelHost.processRequest (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7388:28)
        \_ KernelHost.run (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7328:14)
        \_ Immediate.setImmediate [as _onImmediate] (../lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:7331:37)
        \_ runCallback (timers.js:705:18)
        \_ tryOnImmediate (timers.js:676:5)
        \_ processImmediate (timers.js:658:5)

Environment

• CLI Version :1.38.0 (build d5fa31f)
• Framework Version:1.38.0
• OS :Linux
• Language :Python

Other

My digging led me to the fact that within JSON document of dashboard body generated by CDK there is no annotation for the alarm: "annotations":{"alarms":[]}.

If one were to use regular Alarm, not CfnAlarm, this field is populated correctly:

..."annotations":{"alarms":["'
            - Fn::GetAtt:
                - mycoolalarm677232EC
                - Arn
            - '"]}...

Which leads me to believe that CfnAlarm is not transformed into annotation the right way. Ideally Alarm should support anomaly detection, or if it does - there should be an accessible example.

---

This is 🐛 Bug Report

[oleksii-donoha]

@rix0rrr

I understand that mixing Cfn and L2 constructs isn’t a good idea. But for this particular functionality (alarm based on anomaly detection) there is no L2 support. One other issue https://github.com/aws/aws-cdk/issues/4569 points user to … using Cfn resources.

But there is no CfnAlarmWidget, only L2 AlarmWidget. Alternative way would be to rewrite entire dashboard logic to CfnDashboard, but writing huge JSON document for dashboard body by hand defeats the purpose of using CDK.

I would open feature request to add this functionality to Alarm, but it’s been done in https://github.com/aws/aws-cdk/issues/4569 and it was closed.

@SomayaB should I open separate feature request issue with this use case?

[mrsiejas]

Managed to fix it by moving the dimensions from CfnAnomalyDetector construct to CfnAlarm under metrics parameter

            metrics=[
                aws_cloudwatch.CfnAlarm.MetricDataQueryProperty(
                    id='m1',
                    metric_stat=aws_cloudwatch.CfnAlarm.MetricStatProperty(
                        metric=aws_cloudwatch.CfnAlarm.MetricProperty(
                            metric_name=billing_anomaly_detector.metric_name,
                            namespace=billing_anomaly_detector.namespace,
                            dimensions=[
                                aws_cloudwatch.CfnAlarm.DimensionProperty(
                                    name='Currency',
                                    value='USD'
                                )
                            ]
                        ),
                        period=core.Duration.hours(360).to_minutes(),
                        stat='Maximum'
                    )
                ),